A position sensor, which has the capability of outputting an electrical signal according to a change in impedance of a tubular detection coil caused by a physical displacement of a magnetic core in the detection coil, has been utilized for measurement and control in many technical fields such as internal combustion and electric power facility. In this kind of position sensor, from the standpoint of improving the reliability in detection accuracy, it is desired that the impedance of the detection coil linearly changes depending on the displacement of the magnetic core. However, in fact, as the displacement amount of the magnetic core increases, a deviation from the ideal characteristic occurs, as shown in FIG. 15. To ensure stable detection accuracy, it is proposed to use only a movable range of the magnetic core where the impedance linearly changes. However, when it is important to downsize the position sensor, it is not possible to disregard the other movable range of the magnetic core where the deviation from the ideal characteristic occurs.
For example, International Publication No. WO2004/099727 discloses an improvement in the linearity of coil impedance in this kind of position sensor. That is, it is proposed to effectively improve the impedance linearity that an end portion of the magnetic core is formed thick, or surface-treated with a material having high magnetic permeability, or the number of coil winding turns is increased at an end portion of the detection coil. However, the thickened end portion of the magnetic core leads to an increase in size in a diameter direction of the detection coil, in which the magnetic core is inserted. In addition, since a mechanical resonance frequency lowers due to an increase in weight of the end portion, deterioration in vibration resistance may occur. On the other hand, when a magnetic plating is performed to only a part of a rod-like core, an increase in production cost easily occur in terms of workability and quality control. Moreover, when changing the number of coil winding turns of the detection coil, the structure of a coil bobbin easily becomes complex to prevent the occurrence of disordered winding. In addition, an extension of time needed for an operation of winding a coil wire around the coil bobbin may result in an increase in production cost.